Hello, Your elder daughter had recovered on her own. If she had the same infection with green phlegm and bad oral smell. She had passed the infection to younger one. These infections are notorious to spread through breath or coughing. The younger one is still to develop his own resistance and the infants get a sudden increase in symptoms to take a serious turn. So, I would suggest to take him to a pediatrician for his expert advice for an antibiotic. Till then let him take rest, give him light food, warm water to drink and Coccopin pediatric cough syrup. Paracetamol syrup over the counter. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Vasudha Jayant Athavale